This invention relates to measuring apparatus and more particularly to apparatus for measuring the viscosity of a fluid.
The present invention, while a general application, is particularly well suited for use as a viscosimeter to determine the viscosity of heavy oil or other comparatively viscous fluid at high temperatures and pressures. In the oil and gas industry, for example, accurate measurements often are needed of the viscosity of the liquid hydrocarbons found at some of the shallower depths beneath the surface of the earth, and these materials may have a viscosity as high as 10,000 centipoise. The viscosity should be measured at a temperature and pressure which at least approximate the subsurface conditions to which the material is subjected.
Heretofore, apparatus for detecting the viscosity of a fluid have exhibited a number of disadvantages. As an illustration, several types of prior apparatus for this purpose utilize a capillary tube arrangement to produce a pressure signal corresponding to the fluid viscosity, in which the surface tension of the fluid adversely affected the accuracy of the resulting measurements. In addition, and this has been of special moment in cases in which the viscosity was determined with the fluid under high pressure, the apparatus often was not sufficiently sensitive to detect small changes in the pressure signal. Viscosimeters and similar apparatus of the type previously employed frequently exhibited further difficulties in cases in which it was necessary to make blind viscosity measurements without being able to observe the fluid during the measuring operation.